Some industrial processes, such as those in the petroleum industry, require devices to operate in hazardous atmospheres or other dangerous conditions. Such devices are often governed by an “intrinsically safe” standard, such as the ISA-60079-11 standard, specifying certain conditions for devices in hazardous atmospheres. The conditions seek to either limit the amount of energy stored in device circuitry (e.g., by limiting voltages to capacitors or currents to inductors) or limit the discharge of accumulated energy (e.g., by restricting the spacing of components) such that a discharge of energy will not cause an ignition. Further, in the case of the ISA-60079-11 standard, a circuit must remain safe during normal operation of the circuit even with a certain number of faults.
In some standards, an individual apparatus (or device) is treated differently than an assembly of components that is part of a larger apparatus. In the ISA-60079-11 standard, for example, a shunt safety assembly manufactured as an individual apparatus must adhere to a different section of the standard, as compared with a shunt safety assembly that is part of a larger apparatus. The differing requirements for an individual apparatus can allow manufacturers to produce devices with advantageous properties, such as physically compact packages. However, such self-contained voltage clamping devices can also suffer from failures related to overheating, making them impractical in many applications.